1. Field of the Invention
The present invention relates to a compacting press that includes a system for holding a feed shoe down against a platen, and more particularly, to such a press for making powder metal compacts.
2. Description of the Prior Art
It is known to produce metal parts by compacting metal powder and heating the compacted metal powder to sinter the metal particles to produce a finished metal product. In one type of commercially available compacting press, metal powder is typically delivered to a feed shoe, or shuttle assembly. The feed shoe is movable on the press table between a retracted position and an extended position. In the extended position, metal powder in the feed shoe drops into a die cavity. The feed shoe is then retracted and then upper and lower punches compact the metal powder in the die cavity to form a green compact. A core rod is also extended to form any inner diameter of the powder metal part. The compact is then ejected from the die cavity. When the compact is ejected, the press table lowers and then is raised back to the original level after the compact is removed. More raw metal powder is delivered to the feed shoe, and the feed shoe is extended over the die to feed another quantity of metal powder to the die. The cycle continues as additional green compacts are made.
In such presses, it is necessary to hold the feed shoe against the top surface of the press table or platen to ensure that the metal powder is properly distributed to the die. If the feed shoe were to raise up, an inadequate quantity of metal powder may be fed to the die, and the green metal compact produced could fall below quality criteria.
Two different types of prior art compacting presses are illustrated in FIGS. 9-11. In the type of press 200 illustrated in FIG. 9, the feed shoe 202 is smaller than the feed shoe 302 in the type of press 300 illustrated in FIGS. 10-11. In the FIG. 9 type of press, the feed shoe 202 is typically about 4 inches wide, while the feed shoe 302 of the FIGS. 10-11 type of press may more typically be about 11 inches wide.
In the FIG. 9 type of press, the feed shoe 202 is moved toward and away from a die in the platen 204 and an overlying punch 206 during each cycle of operation. The feed shoe 202 is moved by a pivoting drive mechanism shown in FIG. 9. As the element shown at 208 is pivoted, the feed shoe 202 is pushed or pulled across the platen 204. The feed shoe 202 is held against the platen by a single air cylinder 210 acting against a bridge 212 between two lever arms 214. The air cylinder 210 is behind the feed shoe 202, and behind the feed tube 216 leading to the feed shoe 202. The air cylinder 210 is set at an angle of about 45.degree. from vertical. The FIG. 9 type of press has somewhat limited utility, given the relatively small size of the feed shoe.
In the prior compacting press 300 illustrated in FIGS. 10-11, the feed shoe 302 is moved across the platen 304 by a linear drive. A system of rails and bearings has been used to hold the feed shoe 302 down against the surface of the press table or platen 304. The rails 306 are fixed to the platen 304. Springs 308 push roller bearings 310 up to bear against the rails 306, and the springs 308 push the feed shoe 302 down against the press platen 304, while allowing the feed shoe 302 to be extended and retracted. The rails 306 are long enough so that the feed shoe 302 is pushed against the press platen 304 throughout the range of horizontal motion of the feed shoe 302.
The use of the rails 306, springs 308 and bearings 310 has been problematic. The friction of the bearings 310 against the rails 306 may cause these elements to wear out relatively quickly. Uneven wear can cause part of the feed shoe 302 to raise away from the surface of the press table 304, resulting in uneven powder distribution and poor part quality. Replacement of worn elements has been time consuming, requiring removal of bolts holding the rails 306 to the press table 304.